In color or full-color organic electroluminescent (EL) displays (also known as organic light-emitting diode devices, or OLED devices) having an array of colored pixels such as red, green, and blue color pixels (commonly referred to as RGB pixels), precision patterning of the color-producing organic EL media are required to produce the RGB pixels. The basic OLED device has in common an anode, a cathode, and an organic EL medium sandwiched between the anode and the cathode. The organic EL medium can include one or more layers of organic thin films, where one of the layers is primarily responsible for light generation or electroluminescence. This particular layer is generally referred to as the emissive layer of the organic EL medium. Other organic layers present in the organic EL medium can provide electronic transport functions primarily and are referred to as either the hole transport layer (for hole transport) or electron transport layer (for electron transport). In forming the RGB pixels in a full-color OLED display panel, it is necessary to devise a method to precisely pattern the emissive layer of the organic EL medium or the entire organic EL medium.
A suitable method for patterning high resolution OLED displays has been disclosed in commonly assigned U.S. Pat. No. 5,851,709 by Grande et al. This method is comprised of the following sequences of steps: 1) providing a substrate having opposing first and second surfaces; 2) forming a light-transmissive heat-insulating layer over the first surface of the substrate; 3) forming a light-absorbing layer over the heat-insulating layer; 4) providing the substrate with an array of openings extending from the second surface to the heat-insulating layer; 5) providing a transferable color-forming organic donor layer formed on the light-absorbing layer; 6) precision aligning the donor substrate with the display substrate in an oriented relationship between the openings in the substrate and the corresponding color pixels on the device; and 7) employing a source of radiation for producing sufficient heat at the light-absorbing layer over the openings to cause the transfer of the organic layer on the donor substrate to the display substrate. A problem with the Grande et al. approach is that patterning of an array of openings on the donor substrate is required. Another problem is the requirement for precision mechanical alignment between the donor substrate and the display substrate. A further problem is that the donor pattern is fixed and cannot be changed readily.
Littman and Tang, in commonly assigned U.S. Pat. No. 5,688,551, teach the patternwise transfer of organic EL material from an unpatterned donor sheet to an EL substrate. A series of patents by Wolk et al., U.S. Pat. Nos. 6,114,088, 6,140,009, 6,214,520, and 6,221,553, teach a method that can transfer the luminescent layer of an EL device from a donor element to a substrate by heating selected portions of the donor with a laser beam. Each layer is an operational or nonoperational layer that is utilized in the function of the device.
In these processes a donor containing the electroluminescent materials is heated by radiation and transferred to a receiver, which can already contain a portion of the active device. The device can then be finished by the application of further layers. There is a continuing need for improved lifetime from such devices.